1. Field
The following description relates to a method of accessing optical recording media, and in particular, a method of accessing optical recording media having a multilayer structure, an optical pickup device, and an optical drive using the device.
2. Description of the Related Art
An optical pickup device corresponding to multimedia may be applied to, for example, compact discs (CDs), digital versatile discs (DVDs) and Blu-ray Discs (BDs).
In general, an optical system of an optical pickup device corresponding to multimedia may include an object lens corresponding to CDs/DVDs and an object lens corresponding to BDs, and may further include a beam splitter, a collimator and a mirror. According to structural characteristics of an optical system, an optical system corresponding to CDs/DVDs may have an optical length different from that of an optical system corresponding to BDs, and thus a total optical length required to integrate a plurality of optical systems in one structure has to be ensured to appropriately focus light.
Accordingly, in a conventional optical pickup device corresponding to multimedia, an independent optical system corresponding to CDs/DVDs and an independent optical system corresponding to BDs are simply combined into one structure.
While CDs have one recording layer, DVDs and BDs are each divided into a single layer (SL) type having one recording layer and a dual layer (DL) type having two recording layers.
An optical pickup device applied to these optical recording media has an optical structure corresponding to a DL structure. Conventionally, an object lens optimized for a lower recording layer L0 at a substrate side, or an intermediate layer between the lower recording layer L0 and an upper recording layer L1, is used, and an optical length caused by a difference in position or height of the lower and upper recording layers L0 and L1 may be compensated by shifting a collimator lens disposed behind the object lens along an optical axis. A maximum size of the collimator lens is determined according to the design of the object lens. A maximum effective diameter of the collimator lens, which is used when a beam spot is focused on the upper recording layer L1 may present a problem when forming a small and slip optical pickup device to be used in a notebook computer or a portable ODD.